The present invention relates to means for adjustably setting a pancratic objective having two lens members which are displaceable along the optical axis, the specific context being such an objective for a stereomicroscope. Two lens members subject to different courses of motion are always required in objectives of variable magnification if the focal plane is to be maintained constant during an adjustment of focus.
Known adjusting devices for zoom lenses of stereomicroscopes, such as described, for instance, in published West German Application No. 21 54 977 (Offenlegungsschrift), U.S. Pat. No. 3,502,392 or West German Gebrauchsmuster No. 7,210,832, have a cam cylinder or cam disk which is directly driven by a handle and which has two different cam curves for displacement of the movable lens members with respect to the fixed optical elements and with respect to each other, in accordance with courses of motion which can be calculated in advance. The manufacture of such drives is relatively expensive since two cam curves must be milled with high precision in a well-defined relationship to each other.